Electrically-wound clock



Nov. 5, 1-929. c. I. HALL ELECTRICALLY WOUND CLOCK Filed Nov. 18, 1927 MW 3 a J g m I Imkentovi (llfisscc-zr- 1. Had I, 10y

His Attorney.

Patented Nov. 5, 1929 UNITED STATES PATENT OFFICE CHESTER- I. HALL, OFFORT W AYNE, INDIANA, ASSIGNOR TO GENERAL ELECTRIC COMPANY, ACORPORATION OF NEW YORK ELECTRICALLY-WOUND CLOCK Application filedNovember 18, 1927. Serial No. 234,265.

My invention relates to a constant torque motive mechanism which issuitable for general application but which is particularly adapted foruse in-spring driven clock movements where a small electric motor isemployed for Winding the spring.

The time keeping qualities of the ordinary hand wound spring drivenclock movement are impaired by reason of the fact that the clockescapement is required to regulate the speed between wide limits of themain spring tension. In the eight day clock for example. when the springis fully wound, the escapement mechanism is subjected to considerablymore tension than exists when the spring is nearly unwound. As a resultthe beat of the escapement tends to vary somewhat with the tension ofthe main spring. This varying condition may be compensated for to someextent but at the expenseof added complications and cost. To avoid theconditions above mentioned it has been proposed to maintain the clockspring wound to a substantiall constant tension by automatic means, sucas an electric motor, together with means dependent upon the conditionof the spring for controlling the motor.

My invention relates to improvements in devices, of the last mentionedgroup and its principal object is to provide a simple, inexpensive butreliable mechanism for maintaining the clock spring wound to a veryuniform tension. In carrying my invention into effect I provide meansresponsive to the counter torque of the main spring for controlling thewinding torque transmitted thereto from the winding motor. In thepreferred form of my invention a worm gear is (provided be tween thewinding motor an the spring through which the winding torque istransmitted. There is produced an endwise thrust on the wormproportional to the transmitted torque and the worm is permitted to moveendwise in response to this thrust to control the speed of the drivingmotor, preferably through a friction brake.

The features of my invention Wvhich are believed to be novel andpatentable will be ointed out in the claims ap ended hereto. For abetter understanding my invention reference is made in the followingdescription to the accompanying drawing in which Fig. 1 represents anexpanded perspective View of my invention as applied to a clock; Fig. 2shows the details of the preferred form of the torque controllingmechanism as applied directly to an electric motor of the induction disctype in which the endwise end thrust of the worm shaft is opposed byresilient yielding means such as a spring; Fig. 2 represents an end viewof one of the shaded coil pole pieces of the motor of Fig. 2 with thedisc indicated in dottedlines to illustrate how the. motor torque may beadjusted by adjustment of such pole piece; and Fig. 3 represents anembodiment of the invention where the end thrust of the Worm shaft isopposed by the weight of the worm shaft and the parts carried thereby ina manner to apply a brake to the shaft when the transmitted torquereaches a predetermined desired value.

In Fig. 1 a motor provided with the controlling device of my inventionmaintains a clock spring wound to a uniform tension. The clock springunwinds at a rate determined by an escapement to drive the hands of aclock or to operate any other device at a constant rate. The motorrepresented is an electric motor of the induction disc type comprising ashaded pole stator member 10 and a disc rotor member 11 of conductingmaterial such asaluminum. The details of the motor and its controlmechanism will be explained more fully in connection with Fig. 2. Forthe present it will be 'sufiicient to note that .the disc is caused torotate in the direction of the arrow thereon. The rotor 11 is mounted ona shaft 12 which is provided with a worm gear 13 meshing with a gearwheel 14. Gear 14 is connected through reduction gears 15, 16, 17 and 18to the shaft 19 to which the inner end of the clock spring 20 issecured. The outer end of the clock ,spring is secured to a drum 21rotatively back gear train represented at 26 to the hour hand 27. Theminute hand 27 is mounted directly on shaft 23.

When'the electric motor is energized its armature rotates and winds upthe clock spring through the gear train as represented and the clockspring unwinds to operate the escapement and the clock hands or otherdevices in a well-known manner. No particular form of clock work orescapement is necessary and it will be understood that various changesmay be made in these details without departing from the invention. Thedirection of rotation of the disc 11 and gear 14 represented in Fig. 1will produce a downward thrust on the worm 13 and its shaft 12 as torqueis transmitted from worm 13 to gear 14 and the magnitude of this endwisethrust will of course be proportional to the counter torque of the mainspring 20 as transmitted through the gearing to this point. When themain spring is substantially fully wound the counter torque and the endthrust become sufficient to operate the controlling mechanism and slowdown the motor to a speed just sufiicient to maintain the clock springwound to this particular tension. This controlling feature will now beexplained in connection with Fig. 2.

The induction disc motor stator comprises a U-shaped magnetic frame 28between the parallel arms of which are supported the core pieces 29 and30. The alternating current energizing winding 31 is wound on core piece29 and the two core pieces are separated by an air gap in which the disc11 rotates. Shading coils indicated at 32 and 33 are provided on one orboth pole pieces adjacent the air gap so as to convert the alternating.flux there through to a shifting flux. Where desirable one or both ofthese pole pieces may be adjusted for the purpose of varying the motortorque in the manner indicated in Fig. 2'. The full line position of theshaded coil pole piece represents the maximum flux shifting position inthe direction of rotation of the disc and corresponds to maximum motortorque. The dotted line position of the pole piece represents the natureof the adjustment to reduce the motor torque. Such adjustments can bereadily made for example by loosening the nut shown at 42, Fig. 2, andturning the pole piece in the manner indicated in Fig. 2. The shiftingflux cuts the rotor disc 11 and returns through the magnetic framework28. The shifting flux cutting the disc causes its rotation in awellknown manner. The arallel arms of the framework are extende tosupport the bearings 34 and 35 for the rotor shaft 12. This shaft ispreferably made of non-magnetic ma terial. The upper bearing 34 ismerely a guide bearing which permits the shaft to move endwise. Thebearing 34 is both a guide and thrust bearing the thrust of the shaftbeing against a ball 36 which is backedin the air gap without touchingthe pole pieces. Thiscondition is represented in full lines in Fig. 2.

It will now be apparent that when the disc rotates in a clockwisedirection, as observed from the top, the worm 13 will cause gear 14 torotate in a counterclockwise direction, or-

so that the peripheral portion which meshes with the worm moves upward.If the disc 11 rotates the gear 14 must either turn as indicated by thearrow thereon, or the worm 13 must move downward as indicated by thearrow 13 adjacent thereto. This arrow may represent the end thrustincident to transmitting torque from shaft 12 to gear 14 and is equal tothe counter torque of the clock sprin 20 at this point. This end thrustis opposed by the thrust bearing spring 37. When the clock spring 20,Fig. 1, is in an unwound condition the torque condition between 13 andlaand consequently the end thrust 13 is not suflicient to compress thespring 37 materially, but as the clock spring is wound up and itscounter torque increases, the end thrust also increases and the motorshaft, together with the worm and disc, move downward compressing spring37 until the disc 11 rubs against the lower pole piece 30 and brakes themotor as indicated in dotted lines in Fig.

2. The motor then slows down and rotates condition. The spring 37 ispreferably adjusted so that this condition usuall exists when the clockspring is substantially fully wound. The spring 37 in effect measuresthe tension of spring 20 and the motor is regulated accordingly.

Where cloclzs are manufactured in large quantities it may happen thatthere will be some variation 1n the strength of the clock springsselected for use at 20 and some variation in the characteristics of theescapement mechanism and in some cases these irregularities may be suchthat the proper regulation can not be obtained with the usual escapementadjustment indicated at 25. The adjustment rovided at 37 affords anothermeans of reguating the clock mechanism to a limited extent and permitsthe use of clock springs or escapements which might otherwise have to bediscarded. 'This additional re ulat-ion is possi ble by reason of thefact that by adjusting the sprin tension at 37 I may vary the tension atw ich spring 20 will normally operate and in some cases this may besomewhat less thanthe tension corresponding to a substantially woundcondition.

wound to the tension corresponding to this Instead of allowing the disc11 to rub directly against the pole piece 30 I prefer to face thissurface with a soft friction material which will not scratch the disc ormake any noise. I have found that a piece of paper pasted over the poleface as indicated at 39 gives the desired results. It will be' understood that the forces involved are very small and that this frictionbraking action is not sufiicient to injure the paper or the disc. If thedisc is not exactly true it may alternately start and stop instead ofrunning slowly at a very slow speed when the regulator comes intooperation. In either case the regulation is such that the clock springis maintained at an extremely uniform tension. It will be apparent thatthis regulation is practically independent of variations in motor torquewhich might result from variations in voltage, frequency, wave form, ortemperature. All excess torque of the motor above that required tomaintain the clock spring wound to the desired tension is absorbed bythe friction brake. It will also be evident that this regulation islikewise independent of any inherent variation in the resiliency orstrength of the clock spring 20 such as might occur due to age or totemperature variations. Thus, if the clock spring should graduallyweaken with ageit is sim ly kept wound to a slightly reater amountecause the regulation is epcndent solely upon the counter relationbetween the inner and outer ends of the spring 20.

As a resu t sion the escapement is alwa s subjected to exactly the sametorque con ition and may therefore be of a very simple and inexpensivedesign and still give excellent time keeping energized from a suitablesource of electricity such as the usual lighting circuit as representedin Fig. 1. In case such source of electricity should fail, as it doesoccasionally, the motor will naturally stop. However, the dlock willcontinue to operate until the spring 20 is unwound and I prefer. toemploy a spring that will maintain the clock in operation for about sixhours, if necessary, without rewinding. In the event of a failure'of theelectr i c supply and the consequent failure of motor torque the clockspring can not unwind by driving the motor backward. The worm gear at 13constitutes anirreversible of a constant clock spring ten-' torque andnot upon'any particular rotative I drive and revents any backwardunwinding of the cloc spring.

The motor shaft 12 is shown in a vertical position-in Fig. 2. This isnot essential be end thrust movement would then operateagainst theweight of the shaft instead of with it. The shaft 12 might also beplaced in a horizontal or inclined position.

In Fig. 3 I have represented an embodiment of the invention where theweight of-the rotating parts takes the place of the spring thrustbearing of Fig. 2. In Fig. 3the pitch of the worm 13 is reversed fromthat shown in Fig. 2 so that for the same direction of rotation the endthrust 13 due to the transmission of torque is up instead of down. Whenthis end thrust is sufficient to raise the rotating parts in thebearings the rotating gear '11 comes against a brake 39' and retards thespeed. In Fig. 3 a direct current motor 40 is represented as the drivingmotor and the drive is through a pinion gear 41 instead of being directas in Fig. 2. The brake may be applied at any point in the drive trainbetween the motor and the worm.

The arrangement shown in Fig. 2 comprising an induction disc motor withits armature mounted directly on the worm shaft is the preferablearrangement because of its extreme simplicity and compactness. Likewisethe spring thrust bearing of Fig. 2 is preferable to the weight of Fig.3 because of itsease of adjustment and freedom from positlonrequirements. I have found that with the winding motor of Fig. 2 aconplete clock movement and winding motor may be built and mounted in thesame space ordinarily required for a small hand wound clock movement.The electric motor is preferably mounted between the usual clock platesand serves the beneficial purpose of keeping the clock plate'slightlywarm which is desirable y from the standpoint of lubrication.

In accordance with the provisions of the patent statutes, I havedescribed the principle of operation of my invention, together with theapparatus which I now consider to represent the best embodiment thereof;but I desire to have it understood that the apparatus shownand describedis onl illustrative and that the invention may carried out by othermeans.

Where I have specified a clock movement I intend to include timingmovements in general; for example, the movement is suitablefor operatingtime switches or for driving the chartsof recording instruments at aconstant rate or for establishing the time inmotor comprisin terval fordemand meters and for many other purposes.

What I claim as new and desire'to secure by Letters Patent of the UnitedStates is:

1. In a spring driven clock movement, a driving spring and means formaintaining said spring wound to a uniform tension comprisinganinduction motor having a stationary field member with spaced polepieces separated by an air gap, an armature member mounted for rotationwithin said air gap, a 'shaft on which said armature member is mounted,guide bearings for said shaft which permits limited endwise movementthereof, a worm gear mounted on said shaft and meshing with a gear wheelfor winding up said spring, the arrangement producin an endwise thruston said shaft as the sprlng is being wound, yielding means foropposing'endwise movement of said shaft, the parts being adjusted sothat the armature member moves against one of the adjacent polepieces tobrake the motor when the end thrust exceeds a predetermined amount. 1 v

2. In a spring driven clock movement, a driving spring, and means formaintaining said spring wound to a uniform tension comprising a normallyconstantly energized induction disc motor having a stator member withpole pieces separated by an air gap, an induction disc rotatably mountedin said air gap, a shaft on which said disc is mounted, guide bearingsfor said shaft which permit limited endwise movement thereof, aresilient thrust bearing at one end of said shaft, a

worm gear on said shaft meshing with a gear Wheel for winding saidspring, the direction of rotation of said motor bein such that the endthrust incident to the win 'ng up of said spring is against said thrustbearing, the parts being adjusted so that the armature moves against oneof the adjacent pole pieces to brake the motor as the end thrustapproaches a value correspondingto a predetermined tension of saidspring.

3. In aclock mechanism an induction disc a magnetic frame, pole piecesseparated ya narrow air ga supported in said frame, an energizingwinding for said motor, a shaft having bearings supported in said frame,a disc rotor on said shaft extending into said air gap adjacent the polepieces, the adjacent rotary and stationary parts of said motor comprisina brake for said motor and means for moving said shaft endwise forapplying said brake.

4. In a clock mechanism, an induction disc motor comprising a stationarypart having spaced pole pieces separated by a narrow air gap, anenergizing winding for producing a ,flux across said gap, a discarmature rotatably mounted in said air gap adjacent the faces of saidole pieces, a shaft for said'armature adapte to move endwise 1n responseto the torque of said motor, a brake for said motor comprising theadjacent rotary and stationary'parts of said motor, and a non-metallicfriction surface covering the stationary part of said motor againstwhich the disc moves when the brake is a plied.

'5. In a clock mechanism, an induction disc motor comprising astationary magnetic field member having pole pieces separated by anarrow air gap, an induction disc rotor rotatably mounted in said airgap, and means responsive to the torque of said motor for moving saiddisc in a direction parallel to its axis of rotation so as to bring itssurface against one of the adjacent pole pieces when the motor torqueexceeds a predetermined amount. a

6. In a clock mechanism, an induction disc motor comprising a U-shapedframe, pole pieces separated by a narrow air gap supported between theparallel arms of said frame, a non-magnetic shaft rotatably su portedbetween the arallel arms of said frame, an induction isc armature onsaid shafts-extending into said air gap, said shaft having a limitedendwise movement sufficient to rmit the armature to rub against one of te adjacent pole pieces in the air gap to brake said motor, and meansresponsive to the torque of said motor for controlling the endwisemovement of said shaft.

In witness whereof, I have hereunto set my hand this 15th do ofNovember, 1927.

C HESTER I. HALL.

